Stimulus discrimination

Stimulus Generalization - a response to a specific stimulus becomes associated to other stimuli (similar stimuli) and now occurs to those other similar stimuli.
For Example - a child who gets bitten by black lab, later becomes afraid of all dogs. The original fear evoked by the Black Lab has now generalized to ALL dogs.

Another Example - little Albert (I am assuming you are familiar with Little Albert, so I will give a very general example).
John Watson conditioned a baby (Albert) to be afraid of a white rabbit by showing Albert the rabbit and then slamming two metal pipes together behind Albert's head (nice!). The pipes produced a very loud, sudden noise that frightened Albert and made him cry. Watson did this several times (multiple trials) until Albert was afraid of the rabbit. Previously he would pet the rabbit and play with it. After conditioning, the sight of the rabbit made Albert scream -- then what Watson found was that Albert began to show similar terrified behaviors to Watson's face (just looking at Watson's face made Albert cry. What a shock!). What Watson realized was that Albert was responding to the white beard Watson had at the time. So, the fear evoked by the white, furry, rabbit, had generalized to other white, furry things, like Watson's beard.